1. Technical Field
The present invention relates to an image reading apparatus for reading a surface of a medium.
2. Related Art
Some image reading apparatuses such as scanners include an auto document feeder (ADF) for automatically feeding documents, which are example media. Such image reading apparatuses can automatically feed and read a plurality of sheets of documents. For example, JP-A-2013-184818 and JP-A-2014-058360 disclose such image reading apparatuses.
The image reading apparatuses also include a sensor for detecting the passage of a leading edge of a medium. The image reading apparatus described in JP-A-2013-184818 includes a transport roller 4, which is disposed on the upstream side of an image reading unit 5 for performing reading, and a medium sensor 13, which is provided between the image reading unit 5 and the transport roller 4, for detecting the passage of a medium. When the medium sensor 13 detects the passage of a leading edge of a medium, the medium sensor 13 determines that the medium has reached the transport roller 4 and stops the rotation of a feeding roller 2.
In some cases, a user may erroneously set a batch of documents that are stapled together to an image reading apparatus and its feeding job may be started. In such a case, only the document being in contact with the feeding roller will be fed but the fed document will be deformed due to the stapled portion and may cause a paper jam.
To detect the occurrence of a jam, several techniques have been proposed for known image reading apparatuses. For example, JP-A-2014-058360 discloses a technique for determining whether a jam has occurred in accordance with a sound generated in a document transport path. However, as described above, when a feeding job is executed for a batch of stapled documents and the documents cause a jam, the documents may be irreversibly damaged, for example, tears may be produced. Consequently, the above-mentioned technical problem is not satisfactorily solved only by the known jam determination techniques, and more effective jam determination techniques are required.